Heel pack rock bit



Sept. 17, 1968 A. 0. WHITE 3,401,759

HEEL PACK ROCK BIT Filed Oct. 12, 1966 4 Sheets-Sheet 1 FIGURE 1ANDERSON D. WHITE INVENTOR.

ATTORNEY Sept. 17, 1968 A. D. WHITE HEEL PACK ROCK BIT 4 Sheets-Sheet 2Filed Oct. 12, 1966 ANDERSON D. WHITE INVENTOR.

ATTORNEY Sept. 17, 1968 A. D. WHITE 3,401,759

HEEL PACK ROCK BIT Filed Oct. 12, 1966 4 Sheets-Sheet 4 14(1 INSERTS,No.1) 14 a INSERTS, No.2) l4( 7 lNsERTs, No.3)

1O (12 TEETH) 10' (1a TEETH) 10"(13 TEETH) L/N (INNER ENDS or HEEL TEETH12' (a TEETH) 12"(1 TEETH) 14 (7 INSERTS, No.1) 14 (7 lNsERTs, No.2) 14(7 |NsERTs,No.a) i 1 10 (14 TEETH) lO'ha TEETH) 10"(12 TEETH) (INNER wasTEE or HEEL TEETH 1o,1o',1o")

12'(1 TEETH) v ANDERSON 0. WHITE INVENTOR.

SPEARPOINT "ToRNEY United States Patent 3,401,759 HEEL PACK ROCK BITAnderson D. White, Houston, Tex., assignor to Hughes Tool Company,Houston, Tex., a corporation of Delaware Filed Oct. 12, 1966, Ser. No.586,251 Claims. (Cl. 175-341) The present invention lies in the field ofrolling cutter rock bits adapted to drill holes in abrasive rockformations, and is useful in such drilling even though the strength ofthe rock varies considerably, e.g., from the relatively weak sandstoneand sandy shales to the much stronger limestone, chert and quartzite.Furthermore, such bits are particularly useful in drilling areas ladenwith stringers of abrasive rock which cause heel rounding and severegage wear before the balance of the cutting structure has worn to thesame extent. In some of these instances the gage wear may be uniformwhile in others the wear is mostly near the intersection of the gagesurface and the heel teeth. Sometimes the heel teeth may be worn asseverely as the gage surface, while at other times the deep wear isconfined to the gage and the heel teeth are worn only about the same asthe other rows of teeth.

The bit of the invention is primarily a steel-toothed or milled cutterbit fortified with wear-resistant material such as tungsten carbide onthose areas of the cutters where the abrasive formation is most likelyto cause premature wear, specifically on the gage surface and the heelteeth. The cutting structure inwardly from the heels of the cutters isnot alfected, and consists of the hardened alloy steel teeth known inthe prior art, such teeth being either elementally crested orcircumferentially crested. The heel teeth, however, are modified toprevent rounding in a manner presently to be described.

One prior art attempt to solve the above-mentioned problem was bycompletely eliminating all of the steel heel teeth and replacing themwith a row of heel inserts made of wear resistant material such astungsten carbide, such inserts being formed of tungsten carbide granulescemented or sintered together with a binder of the iron group family,usually cobalt, in the form of quite small cylinders, e.g., A inch% inchdiameter. Since the process for making these inserts involves compactingthe carbide and binder granules together to form the green, presinteredshapes, they have come to be known as compacts, or, more briefly, pacs.These heel inserts were mounted at an angle to both the bottom of thehole and the sidewall, with their flat inner ends buried in the cuttermetal and their blunt cutting tips protruding from the cutter toapproximately bisect the angle between its heel conical surface and itsgage conical surface, much in the manner of the heel inserts of thefirst compact hits, as shown in the original patent to Woods et al., US.Patent 2,687,875.

Such structure did not constitute a satisfactory answer to the problem.Compact bits are sensitive to the formation they are drilling, more sothan milled cutter bits, doing their fastest work in hard formationsthat respond to the chipping-crushing action of their cutting structurebut slowing down to an uneconomical rate in soft formations like shalethat are drilled best by a gouging-scraping type of cutting action. Themilled cutter bits modified so that compacts replaced all of the heelteeth exhibited this same slow drilling rate in soft formations, andsuch use did not make for profitable drilling. (Both types of bits alsoexhibited a similar drilling rate dependence on mud weight, the ratebeing best in low weight muds like 8 /29 /2 pounds per gallon (p.p.g.)but decreasing to a rate slower than that of milled cutter bits when themud weight was increased to the 10-22 p.p.g. range.)

Another disadvantage observed with the prior art bits 3,401,759 PatentedSept. 17, 1968 was that some of them allowed a large uncut rim of rockto form in the bottom of the hole just inwardly from the heel compacts,and such rim grew in radial thickness as drilling continued. Such a rimfurther reduces the drilling rate.

Another prior art structure which may have been aimed in part at therounding problem is illustrated in Schumacher, US. Patent 3,126,067.Schumacher teaches a 3-cone rolling cutter bit in which the primarycutting structure of each cone consists of a multiplicity ofcircumferentially crested steel teeth. There are no elementally crestedsteel teeth, not even in the heel row. Between adjacent circumferentialends of such steel teeth in each row there is a small gap, and in eachsuch gap Schumacher mounts a small tungsten carbide insert, deeplyrecessing it so that the crests of the adjacent steel teeth extend wellbeyond the cutting tips of his compacts. Schumacher uses such insertswith all of his inner and nose rows of teeth as well as his heel teeth,and carries the principle of recessing them so that they terminate shortof the crests of his steel teeth to a logical extreme by spacing hiscocked heel inserts so that they do not intersect his gage surface. SeeFIGURE 3 of the reference.

Thus Schumacher teaches a steel toothed-compact bit in which the Wearresistant inserts do no work whatsoever as long as the steel teethretain their original contours, and it may be assumed that his bit doesa satisfactory amount of drilling so long as no troublesome abrasiveformations are encountered. When abrasive rock is encountered, however,the steel teeth are worn away to expose the cutting tips of the tungstencarbide inserts, and thereafter the bit purportedly will operate insomewhat the same manner as the original compact bits disclosed in theaforementioned U.S. patent of Woods et al., No. 2,687,875.

While Schumachers bit may serve its intended functions well enough, itwill be apparent that its utility is limited by some of the sameconsiderations that limited the usefulness of the aforementioned priorart bit with inserts substituted for all heel teeth. There mustnecessarily be a finite spacing between Schumachers heel teeth and hisfirst inner row of teeth, both of which are circumferentially crestedand are not made overlapping, and in this space there will be an uncutrim of bottom which will grow in size in an abrasive formation and slowthe drilling rate of the bit to an uneconomical level.

In addition, Schumachers heel inserts will not cut gage until part ofthe steel gage surface has been worn away, and by that time the bit willalready be drilling an undersize hole. By contrast, the bit of thepresent invention is operable without permitting the growth of a largeuncut rim of rock, and the limited number of heel inserts assist the bitin drilling a full gage hole from the time the bit is new, beingparticularly useful in prolonging the life of the bit in thosesituations where prior art steel toothed bits become rounded at the heeland lost gage.

In addition to such prior bits, the present inventor and his colleaguesexperimented with a milled cutter fortified with wear resistant insertssecured in each cutter so that they extended normally out to the gagesurface and were there ground flush. Such bits thus had the gagecompacts disclosed in Cunningham, US. Pat. 2,774,570, but otherwise ha-dcutting structure in the form of steel teeth, including all of the heelteeth. They did not solve the problem of heel rounding in the describedtroublesome abrasive formations, but rather permitted the heel teeth towear inwardly and upwardly from the gage point (intersection of gagesurface and crests of heel teeth). A rock ridge or rim grew up frombottom in this area which made the bit slow down to an uneconomicaldrilling rate. The gage inserts worked well enough to prevent excessivegage wear, but these inserts did not help the bit drill a sharp corner.

In the present invention the disadvantages of the prior art bits havebeen overcome by retaining most of the steel cutting teeth, includingthe heel teeth, and partially replacing the others with a limited numberof cocked heel inserts disposed in a recessed fashion so that they outno bottom during the early part of the bit life but rub against thesidewall of the hole to serve a gage-maintaining function from the veryoutset, when the bit is brand new. At the same time, the retained steelheel teeth are all of elemental form to assure a full cutting of thatpart of the bottom adjacent the sidewall of the hole and to eliminateany interrow gaps which could serve as nuclei for uncut rims, even informs of the invention in which the inner rows of steel teeth arecircumferentially rather than elementally crested, such elementallycrested heel teeth sometimes being connected by circumferential webbingand sometimes not. In addition, the retained steel heel teeth areliberally protected on their gage surfaces by a generous application ofwelded-on and ground hardfacing, one preferred form being that disclosedby the undersigned inventor in his co-pending United States applicationS.N. 515,603, filed Dec. 22, 1965.

The present invention may become more clear by considering the followingdetailed description of it in conjunction with the accompanying drawingin which:

FIGURE 1 is a side view of an embodiment of a Hughes Tool Company 7%"diameter WD7 Tricone rolling cutter bit in which all of the steel teethare elementally crested and the adjacent heel teeth are not connected bycircumferential webbing, but rather the outer end of each heel toothextends circumferentially a short distance each way from center so thatthe tooth crest as a whole takes the form of a T,

FIGURE 2 is a bottom view of the bit of FIGURE 1,

FIGURES 3 and 4 are cross-sections of two of the cone cutters of thesame embodiment, respectively of the No. 1 cone and N0. 3 cone, viewedin normal drilling position, the section being taken through one of theheel inserts,

FIGURE 5 is an enlarged fragmentary view of the gage surface of one ofthe cutters of the same embodiment, looking along the axis of rotationof the cutter,

FIGURE 6 is a bottom hole section of the same embodiment, i.e., avertical section through the axis of one of the cutters (No. 1) disposedin operative position, showing in half section through one of the heelinserts the cutting structure of that cutter and also the cuttingstructure of the other two cutters coaxially disposed with cutter No. 1and rotated into the same plane, the number at the upper part of eachtooth indicating the number of teeth in the circumferential row and thenumber in the bottom part indicating the cutter on which that row ismounted,

FIGURE 7 is a bottom hole section, similar to that of FIGURE 6, of asomewhat different bit, a new 7%; inch diameter Hughes WDR Tricone bit,one having cireumferentially crested inner and nose rows of teeth andelementally crested heel teeth, some of the latter being connected bycircumferential webbing, and

FIGURE 8 is a bottom hole section of a bit which when new was identicalto that of FIGURE 7, the FIG- URE 8 bit having been run in the fielduntil its cutting structure was partially worn, as illustrated.

Turning to the FIGURES 1-6 embodiment, which illustrates a 7% inch WD7bit, it will be seen that the general organization of the bit, exceptfor the cutters, is similar to prior art 3-cone rolling cutter bits.Three head sections (not shown separately) are welded together to forman upstanding tapered and threaded shank 5 symmetric about an axis ofrotation 4, and three bit legs 6 are integrally connected to shank 5 andextend downwardly therefrom and out to a somewhat larger diameter. Thebit legs 6 are evenly spaced about bit axis 4, and between each adjacentpair of legs a jet nozzle 8 may be provided to direct a high velocitystream of drilling fluid to the bottom of the hole (although centralizedwater courses located nearer the bit axis may also be used, if desired).From each leg 6 a bearing pin in the form of a short cantilever shaft 26(see FIGURE 6) extends downwardly and inwardly toward bit axis 4, and itis on these shafts that cutters 1, 2 and 3 are rotatably mounted so thatthey rotate about the individual shaft axes 27 and roll over the bottomof the hole as weight and torque are applied to the bit. Bearings forthe cutters are illustrated in FIGURE 6 as consisting of rollers 22,balls 23, a nose bushing 24 and a thrust button 25, but the bearingsform no part of the present invention and it is to be understood thatany suitable combination of journal and non-friction bearings foundsuitable with prior art bits may be employed, and may or may not beprovided with any of several lubricating systems, sealed or unsealed.

The cutters themselves have cutting structure not appreciably differentfrom that heretofore known except at the heel and gage. Thus No. 1 conehas a spearpoint 9 and an annular inner row 11 of elemental steel teethdiscretely spaced from one another, No. 2 cone has a nose row 15 and aninner row 17 of similar teeth which follow the corresponding rows of theNo. 1 cone, and No. 3 cone has a nose row 19 and an inner row 21 whichfollow rows 15 and 17 of the No. 2 cone, the distribution being suchthat, as best seen in FIGURE 6, the teeth in rolling over the bottomform tracks lying between the tracks formed by the teeth on the othercutters and thus cooperate to cut the entire bottom except for the verynarrow upwardly converging rims 30 which disintegrate readily undernormal drilling conditions. The crests of these nose and inner rows ofteeth collectively form a conical surface generally referred to by bitdesigners as the main or bottom cutting surface, while the crests of theheel teeth on all cutters is known as the heel cutting surface.

The structure of the invention lies entirely in the heel or outermostrow of teeth and the gage surface of the cutters, and by again referringto FIGURES 1-6 it will be seen that the heel cutting structure comprisesfull length or retained T heel teeth 10, 10' and 10" on cutter No. 1,No. 2 and No. 3, respectively, and partially cutaway heel teeth 12, 12'and 12" which were originally of the same full crest lengths as teeth10', 10' and 10", respectively, but have had their outermost portionscut away to leave spaces adjacent the gage surface in which inserts 14are mounted. In some cases, when an original tooth has only a shortlength of crest, it may be completely eliminated to make room for aninsert. (This condition is not shown in the drawing, wherein the heelteeth of the different cones vary in crest length, No. 1 cone hav' ingthe longest crests which are so long that they are relieved by notches13 to divide heel teeth 10 into inner parts and outer parts, as shown.The shortened heel teeth 12 simply have these outer parts removed.) Thegeneral plan in the design illustrated was to leave two of teeth 10 (or10 and 10" on the other cones) intact and modify every third one for themounting of an insert 14. Such inserts are inclined with respect to boththe gage surface 18 and the heel conical cutting surface of the cutterdefined by the crests of the heel teeth, and it will be apparent thatinserts 14 are disposed with their cutting tips 16 extending downwardlyfrom the cutter toward the heel conical surface and the bottom of thehole a considerably lesser distance than steel heel teeth 10 (or 10' or10"), and thus that they cut no bottom while such teeth are new. It willalso be apparent from the sectional view that the inserts extend to gagesurface 18 and are ground flush at 20 with such surface, and thus thatthey bear against the sidewall of the hole and help drill it to apredetermined diameter even when the bit is new. The surface of thecutter body through which insert 14 extends is preferably flat andnormal to the longitudinal dimension of the insert, as shown at 28 and29 for cutters No. 1 and No. 3,

respectively, (FIGS. 3 and 4) to equalize stresses on the insert andminimize the likelihood of breakage.

The gage surfaces 18 of retained heel teeth 10, and 10" are providedwith a welded-on tungsten carbide hardfacing (not visible), desirableforms thereof being disclosed in the abovementioned co-pendingapplication of the present inventor. This surface hardfacing supplementsinserts 14 in bearing against the sidewall of the hole and keeping itdressed to a uniform diameter.

The manner in which bits of the present invention prevent cutting abottom pattern to leave an uncut rim adjacent the sidewall of the holewill be evident from FIG- URE 6, and this same figure illustrates why itis desirable to retain some of the heel teeth intact and make such teethwith elemental crests rather than circumferential crests. In theillustration the retained heel teeth 10, 10' and 10" are shown inphantom to avoid confusing them with modified or stub heel teeth 12, 12'and 12", but they extend radially inwardly (toward the right in thedrawing) so that they terminate at the locations marked on the drawing.These rows of heel teeth overlap one another so there is no gap in thebottom cutting structure, and thus no uncut rim is allowed to be formed.It can be appreciated that if all heel teeth were modified and replacedwith inserts, such a rim could be started between inserts 14 and thestub heel teeth 12, 12' and 12", especially in one of the aforementionedabrasive formations that promote gage wear and heel rounding. What wouldmake this particularly likely to happen is the fact that there would beno teeth directly under inserts 14, the bottom pattern of the rock wouldcurve around the modified heel teeth to a raised step out by theinserts, and the outer ends of heel teeth 12, 12' and 12" would beexposed to erosion. By the same token, a bit in which the heel row ofeach cutter consisted entirely of inserts would have nothing but theseinserts drilling on the outermost ring of the bottom at all times, andwould drill the softer formations only at slow and uneconomical rates.

FIGURES 7 and 8 are bottom hole sections similar to that of FIGURE 6 butdiffering therefrom in that the bit of FIGURE 7 is a new bit in whichall of the inner and nose rows of teeth are circumferentially crested,and most of the adjacent retained heel teeth are joined bycircumferential webbing at the gage surface (the latter detail not beingapparent in FIGURE 7). The bit of FIGURE 8 is identical with that ofFIGURE 7 except for the fact that it has been used in drilling hole tosuch an extent that all of the steel teeth are partially dulled.

These two figures illustrate the effectiveness of the invention becausethey show that the partially dulled bit of FIGURE 8 is still capable ofdrilling a full-gage hole despite its worn condition. This bit, SerialNo. DS171, had drilled 144 feet of hole during 8% operating hours at thetime it was pulled and used for the drawing illustration, most of thedrilling taking place through abrasive limestone which included a gageproblem section of Kansas City lime, the drilling having taken place inthe Camrick field of Beaver County, Okla. (PSR 1482). Prior art bitshaving no inserts 14 and being like that of FIGURES 7-8 except that allsteel heel teeth are retained are likely to drill somewhat less footagewhen used in the same location, and when pulled are highly likely toshow evidence of heel rounding, excessive gear wear, or both. This mayrequire the following bit to ream a considerable portion of the holebefore touching bottom.

A comparison of FIGURES 7 and 8 will show that maximum wear has takenplace on the heel teeth, as the spearpoint and inner rows of teeth areworn to a considerably lesser extent. Inserts 14 have barely begun todrill the bottom of the hole, and there is thus considerable liferemaining to the bit. Despite the extended use, the same field report(PSR 1482) mentioned above discloses that the diameter of the bit gage7.850 inches after use.

Another bit like that in FIGURE 7 was used in drilling abrasivelimestone in the Caprock field of Lea County, N.Mex., and drilled 114feet in nine hours through a formation which included a zone of chertylimestone known as the Wolfcamp without loss of gage. (Bit No. HT 148,or PSR Report 1520.) At this same location and depth milled cutter bitswithout the features of the invention normally make less than feet andlose gage.

As yet another example, a bit like that in FIGURES 1- 6 drilled theabrasive and gage-wearing Kansas City lime in Grant County, Kans.,drilling 200 feet in 11 hours to maintain a full gage hole. Average runsfor milled cutter bits in the same formation of this area are feet in12% hours, with loss of gage.

There has thus been disclosed an improved steeltoothed bit havingelemental heel teeth in which the drilling performance in abrasiveformations is improved by at least partially removing the outer portionsof some of the heel teeth and substituting for them inserts ofwearresistant material disposed so that their cutting tips extend to thegage surface but extend only slightly toward the heel conical surface ofthe cutter, terminating well below the crests of the adjacent heelteeth. While the work has involved thus modifying only /3 of the heelteeth, nothing critical about such number is known, and it can probablyvary widely so long as a substantial number are retained intact.Similarly, there appears to be nothing critical about the relativeprotrusions of the inserts and the adjacent heel teeth from the body ofthe rolling cutter, so long as the cutting tips are exposed to bottomcutting action at the time the adjacent heel teeth are close to the endsof their useful lives.

What is claimed is:

1. A rolling cone cutter having a body with a gage surface and annularrows of crested steel cutting teeth protruding from the body so that thecrests will out the bottom of a hole, the outermost or heel row thereofbeing modified so that a part of the teeth therein are at leastpartially removed and replaced with inserts of hard, wearresistantmaterial disposed so that their cutting tips extend all the way to thegage surface of the cutter but lie closer to the cutter body than thecrests of adjacent heel teeth.

2. A rolling cutter for rock bits having a body, a conical heel cuttingsurface and a conical gage surface intersecting and coaxial with saidheel cutting surface, an annular row of circumferentially spacedelementally crested steel cutting teeth defining said heel cuttingsurface, some of said heel teeth being unmodified and extending to saidgage surface while the others are modified so that their gage portionsare cut away, and a heel insert mounted in the space left by saidcutaway portion, said insert being mounted with its base portion securedin said cutter spaced from both said conical surfaces and its cuttingtip protruding from the cutter to intersect said gage surface but to liecloser to the cutter body than the crests of said steel teeth.

3. A rolling cutter comprising a body having a conical main cuttingsurface, a conical heel cutting surface and a conical gage surface, saidconical surfaces being coaxial about a common axis and said heel andgage surfaces intersecting each other, said main and heel cuttingsurfaces being defined by the crests of a number of annular rows. ofcutting teeth extending outwardly from said cutter body, said rowsincluding an outermost or heel row of elementally crested teeth of whicha substantial number extend to said gage surface and the remainder areseparated from said gage surface by spaces, and a wear resistant insertsecured in the cutter body inclined with respect to said heel and gagesurfaces and with its cutting tip protruding therefrom in each saidspace adjacent the intersection of the surfaces, and spaced above theheel surface, said insert terminating flush with said gage surface andextending from said cutter body less than the crests of the adjacentheel teeth.

4. A rolling cutter having a body with a comparatively elongated conicalbottom cutting surface, a shorter conical heel cutting surface and ashorter conical gage surface, said conical surfaces being coaxial abouta common axis of rotation and said heel and gage surfaces intersectingone another approximately at a right angle, annular rows of cuttingteeth integral with said body and extending from said body so that theircrests define said bottom and heel cutting surfaces, said rows of teethbeing coaxial with said axis of rotation and spaced from one anotheralong said axis, said rows including an outermost or heel row of teethof which a substantial number extend to said gage surface and are thereprovided with a wear-resistant hardfacing ground flush with said gagesurface, the balance of the teeth in said heel row being modified byremoving at least the outer portions thereof to leave spaces adjacentsaid gage surface, and wear resistant insert secured in the cutter bodyat each such space, said insert being disposed to approximately bisectthe angle between said gage surface and said heel cutting surface, saidheel teeth extending from said bottom surface beyond the cutting tips ofsaid inserts.

5. A rolling cone cutter for rock bits comprising a body with a conicalbottom cutting surface, a conical heel cutting surface and a conicalgage surface intersecting said heel surface, a multiplicity of rows ofsteel teeth extending from said body with their crests forming saidbottom and heel cutting surfaces, said rows including a heel row ofelementally crested teeth of which a substantial number extend to saidgage surface and are there provided with a welded-on hard facing oftungsten carbide ground flush with said gage surface, some of saidsubstantial number of heel teeth being separated from one another bycircumferential spaces, and an insert secured in the cutter body at eachsuch space so that its cutting tip protrudes therefrom and extends allthe way to said gage surface but lies closer to the body than the crestsof the adjacent heel teeth.

6. In a rolling cone outter for rock bits having annular rows of steelteeth protruding from the cutter body, including a row of elementallycrested heel teeth extending to the gage surface thereof, theimprovement comprising a substantial number of said heel teeth having atleast their outer portions cut away to define spaces adjacent said gagesurface and a wear resistant insert secured in the cutter body at eachsaid space with its cutting tip intersecting said gage surface, saidcutting tip being ground flush with said gage surface and extending fromthe cutter body less than the adjacent heel teeth.

7. In a steel-toothed rolling cone cutter for rock bits in which theheel teeth are elementally crested, the improvement in which the numberof said heel teeth extending completely to the gage surface issubstantially reduced and some of such heel teeth are separated fromeach other by spaces, and an insert secured in the cutter at each saidspace so that its cutting tip lies closer to the body than the adjacentheel teeth and extends to and is flush with the gage surface of thecutter.

8. In a rolling cone cutter for rock bits having a conical main-bottomcutting surface, a conical heel cutting surface and a conical gagesurface, and annular rows of steel teeth extending from the cutter withtheir crests forming said cutting surfaces, including a row ofelementally crested heel teeth, the improvement comprising dividing saidheel teeth into a first substantial number which extend to said gagesurface and are there provided with a welded-on ihardfacing of tungstencarbide, and a second substantial number having at least their portionsadjacent said gage surface cut away to define spaces adjacent suchsurface, and wear resistant inserts of tungsten carbide secured in thecutter at such spaces so that their cutting tips extend toward said gageand heel surfaces, said cutting tips extending from the cutter andterminating short of said heel cutting surface and being ground flushwith the gage surface.

9. In a rolling cone cutter for a rock bit, such cutter having a bodywith a conical heel cutting surface and a conical gage surface, suchsurfaces being coaxial and intersecting each other at about a rightangle, said cutter having cutting structure extending from said body todefine said heel cutting surface, said cutting structure consisting ofan annular row of steel cutting teeth, the improvement in which said rowof heel cutting teeth consists in part of a substantial number ofelementally crested steel teeth which extend to and intersect said gagesurface and are there provided with a hardfacing of tungsten carbide,said heel teeth being circumferentially spaced from one another todefine spaces adjacent said gage surface, and consisting in part of asubstantial number of wear resistant inserts secured in the cutter bodyat such spaces, each said insert having a cutting tip protruding fromthe bit body and being ground flush with said gage surface, theelemental crests of said heel teeth being spaced further from saidcutter body than said cutting tips of the inserts.

10. In a steel-toothed rolling cone cutter having a gage surface and anintersecting heel cutting surface defined by the crests of an annularrow of elementally crested steel cutting teeth protruding outwardly fromsaid cutter, the improvement comprising fortifying said heel teeth witha number of wear resistant inserts by terminating a substantial numberof said heel teeth short of said gage surface to leave spaces adjacentsaid surfaces, said inserts being mounted in the cutter at such spacesso that their cutting tips protrude from the cutter a lesser extent thanthe heel teeth and extend to and are ground flush with said gagesurface.

References Cited UNITED STATES PATENTS 2,887,302 5/1959 Garner 175-3742,907,551 10/1959 Peter 175375 2,990,025 6/ 1961 Talbert l378 X3,126,067 3/1964 Schumacher 374 3,134,447 5/1964 McElya 175-332 NILE C,BYERS, 111., Primary Examiner.

8. IN A ROLLING CONE CUTTER FOR ROCK BITS HAVING A CONICAL MAIN-BOTTOMCUTTING SURFACE, A CONICAL HEEL CUTTING SURFACE AND A CONICAL GAGESURFACE, AND ANNULAR ROWS OF STEEL TEETH EXTENDING FROM THE CUTTER WITHTHEIR CRESTS FORMING SAID CUTTING SURFACES, INCLUDING A ROW OFELEMENTALLY CRESTED HEEL TEETH, THE IMPROVEMENT COMPRISING DIVIDING SAIDHEEL TEETH INTO A FIRST SUBSTANTIAL NUMBER WHICH EXTEND TO SAID GAGESURFACE AND ARE THERE PROVIDED WITH A WELDED-ON HARDFACING OF TUNGSTENCARBIDE, AND A SECOND SUBSTANTIAL NUMBER HAVING AT LEAST THEIR PORTIONSADJACENT SAID GAGE SURFACE CUT AWAY TO DEFINE SPACES ADJACENT SUCHSURFACE, AND WEAR RESISTANT INSERTS OF TUNGSTEN CARBIDE SECURED IN THECUTTER AT SUCH SPACES SO THAT THEIR CUTTING TIPS EXTEND TOWARD SAID GAGEAND HEEL SURFACES, SAID CUTTING TIPS EXTENDING FROM THE CUTTER ANDTERMINATING SHORT OF SAID HEEL CUTTING SURFACE AND BEING GROUND FLUSHWITH THE GAGE SURFACE.